2. The Mole Revision from S.G. 1 mole is the formula mass in grams. Concentration of solutions is measured in mol/l. We use moles to Balance equations. Example – Calculate the mass of 0.5 moles of Water. Formula mass = H 2 O = 2 + 16 = 18 1 mole = 18 g, 0.5 moles = 0.5 x 18g = 9g

3. Avagadro’s Constant (L) 1 mole of any substance contains the same amount of “ elementary entities” as 12g ( 1 mole) of C – 12. “ Elementary entities” can be; atoms, molecules, ions, units, protons, electrons etc. Avagadro’s constant = 6.02 x 10 23 mol/l.

4. Example Water – H2OH2O How many molecules are in 1 mole – 18g- of water? 1 x L = 6.02 x 10 23 molecules. How many atoms in 1 mole – 18g – of water? Each molecule is made of 2 H and 1 O atoms – a total of 3 atoms. 1 mole of water contains 3 x L = 3 x 6.02 x 10 23. = 1.8 x 10 24 atoms

5. Water cnt. How many molecules are there in 0.5 moles of water? 1 mole = 1 x L 0.5 moles = 1.5 x l x L = 0.5 x1 x 6.02 x 10 23. »= 3.01 x 10 23 molecules How many atoms are there in 0.1 moles of water? In 1 mole there are 3 x L atoms. In 0.1 moles – 0.1 x 3 x L = 0.1 x 3 x 6.02 x 10 23 = 1.8 x 10 23 atoms

6. More examples How many protons are there in 1 mole of carbon? In 1 atoms of Carbon there are 6 protons( atomic number) In 1 mole there will be 6 x L protons = 6 x 6.02 x 10 23 = 3.6 x 10 24 protons. How many protons are there in 0.1 moles of Carbon? 1 mole = 6 x L 0.1 moles = 0.1 x 6 x L 0.1 x 6 x 6.02 x 10 23 = 3.6 x 10 23 protons.

7. Molar Volume The average Molar Volume of a gas can be taken as 22.4 l – at the same standard temperature and atmospheric pressure. We can calculate molar volume using the following: M DV M = mass, D = Density, V = Volume

8. Worked Examples! Data: Mass of empty flask = 107.49g Mass of flask + Carbon dioxide = 108.37g Volume of flask = 480 cm 3. Calculate – Mass of CO 2 = 108.37 – 107.49= 0.88g. 0.88g of CO 2 has a volume 0f 480 cm 3.

9. The Answer! What about 1 mole? I mole of CO2 = 44g 44g has a volume of: 44/0.88 x 480 = 24,000 cm 3 The molar volume of Carbon dioxide is 24,000 cm 3 or 22.4 litres.

10. Calculating Density Example Calculate the density in g /l of Neon, molar volume – 24l. D = M/V D = 20.2/24 D = 0.84 g/l

11. Density cnt Calculate the density of Ammonia gas in g/cm3, molar volume 24 l. D = M/V D = 17/24 D =0.71g /l or 0.00071g / cm3

12. Calculate the molar volume of Argon if it has a density of 0.0018g cm 3 V = M/D V = 40/0.0018 V = 22, 222cm 3 or 22.2 l

13. Calculations using gas volumes Calculate the volume and composition of the residual gas mixture when 20 cm 3 of methane is burned completely in 100cm 3 of Oxygen. CH 4 + 2O 2 —> CO 2 + 2H 2 O 1 mole : 2 moles 1 mole : 2 moles 20 cm 3 : 40 cm 3 20 cm 3 : 40 cm 3 The residual gas mixture will contain: 20 cm 3 CO 2, 40 cm 3 H 2 O and 60 cm 3 un reacted oxygen.( The Oxygen is in excess!)